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Retroactive reinsurance contracts (Tables) | 9 Months Ended
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Sep. 30, 2025
Insurance [Abstract] |
Reconciliation of changes in claim liabilities and incurred losses and loss adjustment expenses | Reconciliations of the changes in estimated liabilities for retroactive reinsurance unpaid losses and loss adjustment expenses follow (in millions).
| 2025 |  |  | 2024 |
Balance at the beginning of the year | $ | 32,443 |  |  | $ | 34,647 |
Losses and loss adjustment expenses incurred | 13 |  |  |  | (66 | )
Losses and loss adjustment expenses paid |  | (1,259 | ) |  |  | (1,596 | )
Foreign currency effect |  | 110 |  |  |  | 75 |
Balance at September 30 | $ | 31,307 |  |  | $ | 33,060 |
Losses and loss adjustment expenses incurred | $ | 13 |  |  | $ | (66 | )
Deferred charge adjustments |  | 499 |  |  |  | 610 |
Losses and loss adjustment expenses incurred, including deferred charge adjustments | $ | 512 |  |  | $ | 544 |

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- Definition Schedule of liability for unpaid claims and claims adjustment expense and incurred losses and loss adjustment expenses retroactive reinsurance contracts. + References No definition available. + Details
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Namespace Prefix: | brka_
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Balance Type: | na
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_InsuranceAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration